1. Field of the Invention
This invention relates to an improved structure of pushbutton in keyboard, more particularly, to a pushbutton containing a link (bridge) jointedly disposed on a printed circuit board directly for building a lower cost waterproof keyboard in thinner thickness.
2. Description of the Prior Art
The structure of an existing keyboard shown in FIG. 1 mainly comprises a key cap, an elastomer, a link (bridge) laid surrounding the elastomer, a plastic assembly-jointing board made by injection molding, a membrane printed circuit board (abbreviated as PCB hereinafter), and a base underneath the PCB, wherein the assembly-jointing board is pressed out to form a pivot-jointing portion on its surface for pivotally jointing with a movable shaft of the link; and a key cap is combinably jointed onto the link to complete a known structure of keyboard.
Another type of keyboard structure is shown in FIG. 2. The keyboard comprises a key cap, an elastomer, a link, a membrane circuit board, and a base, wherein the base is pressed out to form a plurality of pivot-jointing portions on its surface for pivotally jointing the link. When assembling, the procedure is to overlap the membrane circuit board on the base firstly, then, position and fix the elastomer, pivotally joint a movable shaft of the link to the pivot-jointing portion, and finally, combinably joint the key cap on the link to complete a keyboard.
The defects of the foregoing keyboard may be summarized as the following:
1. For pivotally jointing the link, the assembly-jointing board or the base must be pressed out to form a plurality of pivot-jointing portions at certain height that thickens the keyboard and increases the production cost due to the additional pressing process.
2. As the base is a metallic rigid body, the movable shaft may be deformed or ruptured when it is to pivotally joint the link with the pivot-jointing portion to result in waste of resources occasionally.
3. After use in a long-term period, the movable shaft of the link and the pivot-jointing portion of the metallic base fret each other frequently to create metal dust that can possibly drop on the PCB to incur a short circuit or a malfunction.
4. As two printed circuit layers of abovesaid membrane PCB and an insulation layer are overlapped merely, the space therein keeps open without sealing, and when the elastomer is pressed downwards while a user happens to drip a water drop down to the keyboard, the water drop will be sucked into the inlayers through clearance in the PCB as soon as the elastomer is released due to a vacuum suction effect, which may result in a short circuit.
In view of the above imperfections, this invention is proposed to form a pivot-jointing portion on a PCB directly by extrusion for pivotally jointing a movable shaft of a link in order to provide a lower cost, thinner, waterproof keyboard.